The use of stereotaxic radiosurgery to render tissue, particularly tumorous tissue, necrotic is well known. In general, this technique has been utilized for brain surgery but has not been used for surgery elsewhere in a patient's body. The reason for the limitation to brain surgery is that if the beam is to be properly aimed or focused onto a target region which is to be rendered necrotic, it is necessary to provide an external radio-opaque frame which is in a fixed position relative to the targeted region. The frame is precisely positionable in space and provides a reticle which can be observed by passing diagnostic x-ray beams through the frame and through a region of the body which includes the target region to be irradiated thereby allowing the position of the patient or of the beaming apparatus to be adjusted so that it is properly focused upon that region. Most portions of the body do not have available bone structure to which such a frame can be readily attached.
Stereotaxis is a branch of neurosurgery that utilizes spatial information provided by neuroradiologic studies to treat certain disorders of the central nervous system with great accuracy. Conventional stereotaxis, as mentioned above, uses an external frame anchored with screws to the patient's skull as a frame of reference for both localizing (by radiologic studies) and treating intracranial tumors and malformations. Stereotaxic radiosurgery builds on this concept by combining the precise localizing capabilities of stereotaxis with a high-energy radiation source. Over the past twenty years several independent groups have utilized radiosurgical techniques to treat a variety of brain disorders with single large fractions of radiation. In contrast to conventional radiation therapy (where the target tissue and the surrounding healthy tissue are substantially equally exposed to radiation and the healthy tissue is expected to have a higher resistance to radiation damage), the rationale behind such a procedure is that eventually radionecrosis will be produced at the targeted site. Because the outcome of this procedure is theoretically the same as standard resective surgery, the term radiosurgery was coined. The constantly growing list of indications for radiosurgical treatment includes arteriovenous malformations, acoustic neurinomas, metastatic lesions, unresectable skull base meningiomas, and several types of tumors involving the brain stem, pituitary and pineal region. Even Parkinson's disease and obsessive-compulsive disorders have been treated at the Karolinska Institute in Stockholm by creating well-circumscribed necrotic lesions in discrete brain locations. In many clinical situations stereotaxic radiosurgery is widely acknowledged as the treatment of choice.
The radiosurgical principle of confining radiation as much as possible only to the volume of a brain tumor is both a significant and timely concept. Meanwhile, the development of new technologies and the favorable clinical results that have been observed has lead to dramatic increases in the numbers of patients currently being treated with stereotaxic radiosurgery. Although exact figures are impossible to find at this point, reports in the literature and discussions with experts in the field of radiosurgery suggest that already several thousand patients per year, worldwide, are being treated with this technique. Despite such growing enthusiasm for stereotaxic radiosurgery, numerous theoretically attractive uses of such therapy remain impractical because of limitations in current instrumentation.
Although conventional stereotaxic radiosurgery combines a necrosing dose of energy largely to the lesion in question, there are limits to this capacity (regardless of radiation source) and inevitably normal brain is in some measure also irradiated. Overall, the smaller the volume of brain that is irradiated, the less the risk of healthy tissue radionecrosis. In the ideal situation, i.e., the treatment of very small volume lesions, normal tissue tolerance is not an issue for radiosurgeons. However, for both radiophysical and radiobiological reasons, radiosurgical treatment of the more frequently encountered larger lesions is problematic. With a risk that is proportional to both dose and the volume irradiated, radiation neorosis of the brain adjacent the treated lesion remains the major complication of stereotaxic radiosurgery. Consequently, despite the precision of stereotaxic radiosurgery, the normal tolerance to a large single dose of radiation is often a concern and strict attention must be paid to dose and volume parameters. This holds true for every radiosurgical technique regardless of radiation source.
The apparatus and method of the present invention have several advantages over other currently available radiosurgical systems. In particular, when operating in accordance with the present invention it is possible to perform multiple fraction radiosurgical treatment (separating the overall dose into a plurality of fractional doses and delivering the fractional doses hours or even days or weeks apart) utilizing the apparatus and method of the present invention. Consequently, a new type of ionizing radiation therapy is provided for brain tumors, one that blends conventional radiation therapy techniques with surgical principles of accurate anatomic localization. Presently there is no practical method for delivering multiple fraction precision radiation treatment to brain tumors because a frame must be left attached to the patient's skull with screws for the entire time of treatment which may desirably be weeks if one is attempting to minimize healthy tissue radioneorosis. In making precise multiple fraction therapy feasible, widespread application of the technique is possible in the treatment of the many tumors that are currently poorly treated with either surgery or radiation therapy.
The problems encountered in the radiosurgical treatment of the more frequently encountered larger lesions have provided much of the impetus for development of the present invention. Although the intent of the conventional stereotaxic radiosurgical treatment is to induce radionecrosis throughout the entire volume of a targeted tumor or malformation, one is limited by the above-described radiophysical and biological problems. Fractionated radiosurgery, which can be carried out using the apparatus and method of the present invention, is intended to accomplish the same objective, yet normal brain immediately adjacent to the tumor inherently receives a more tolerable dose and fraction. The total dose of radiation to the tumor can be pushed high enough to induce necrosis, yet still provide normal tissues, which received much less radiation, enough time for cell repair. Comparison between the cell kinetics of normal brain and the lesion being treated are only relevant as they pertain to this issue. It is critical to keep in mind that normal brain is relatively tolerant of even very high radiation doses delivered to small volumes. Furthermore, since in one reported instance a patient died from acute uncontrollable tumor and brain edema immediately following stereotaxic irradiation of a large tumor, there should be a benefit to inducing gradual neorosis in large tumors with fractionated therapy.
Despite the theoretical benefits of fractionated radiosurgical treatment, current techniques of stereotaxic localization precludes such an approach. Specifically, the major obstacle is a need for an external frame, attached to the patient's head with screws, which is impractical, if not impossible, to keep in place over the several days to few weeks needed to carry out such a therapy. Since the present invention does not rely on rigidly connected frames, it readily circumvents this problem. In addition, the computer mediated stereotaxic radiosurgery of the invention, with minor modifications, opens up the possibility of using radiosurgery outside the cranium, a thoroughly unexplored concept. Given the phenomenal development of new imaging techniques over the past fifteen years, there is now the means to visualize accurately nearly all body structures, and as a consequence, it seems reasonable that stereotaxic radiosurgical principles shall be of benefit in the treatment of non-brain neoplasms as well. Furthermore, since stereotaxic radiosurgery often provides a substitute for resective surgery, its utilization will lead to major savings for society.
As is apparent from the above discussion, it would be desirable to have a stereotaxic radiosurgical instrument which would be capable of use elsewhere than for brain surgery, which indeed could be used to excise non-tumorous tissue such as glands, if desired, which would operate with substantially no patient discomfort and which would make possible the convenient and safe use of doses of radiation accurately delivered in separate fractions, if need be, over a total elapsed time period of several day or weeks.
It is also desirable to be able to properly and accurately align other surgical instrumentation, e.g., a biopsy probe which can then be extended linearly into a patient up to a tumor or the like where sampling can be performed.